Have you pulled apart the electrical unit? If not, take it apart and clean all the metal points as they get bugged up with crap. Its a lot of small parts, but very logical. Just be careful when you open it up.

Otherwise if that fails, it is probably the motor.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k